Study On The Charm Quark Tagged Jets In High Energy Heavy Ion Collisions

In the Standard Model(SM)of particle physics,it is believed that the protons and neutrons are composed of smaller constituents—quarks and gluons.The strong interactions between quarks and gluons are described by Quantum Chromodynam-ics(QCD)theory.Due to the fact of color confinement in QCD,we can not see free quarks and gluons in nature.It is expected that high-energy heavy ion collisions will generate a new state of matter,Quark-Gluon Plasma(QGP),at such hot and dense condition.The high-energy nuclear collisions at The Relativistic Heavy Ion Collider(RHIC)of the Brookhaven National Laboratory in the United States and the Large Hadron Collider(LHC)of the European Nuclear Center provide a way to study the properties of QGP.Jets and heavy quarks(charm,bottom)serve as two excellent hard probes of the QGP fireball in relativistic heavy-ion collisions.The energetic out going parton produced in the hard scattering split and hadronise into a collimated spray of particle,namely jets.High energy partons traverse the hot and dense QCD matter(QGP medium)and strongly interact with the constituents of the QCD matter,leading to the parton energy loss,called "jet quenching" effects.Due to their large masses,heavy quarks are mainly produced via hard scattering at the early stage of relativistic heavy-ion collisions.Hence the heavy quarks are witnesses of the entire bulk medium evolution,therefore being ideal probes to the properties of QGP.The studies on heavy flavor jets,which combines heavy quarks in-medium inter-actions and jet inner structures,are promising in high-energy nuclear physics.The advantage of heavy quarks jets is that the final state observables are hardly affected by the non-perturbative hadronization processes.To study the in-medium parton transport,we use the PYTHIA6 to provide the pp-baseline,and employ modified Langevin equations to update the position and momentum of partons.The medium induced gluon radiation are implemented by the Higher-Twist radiation spectrum,and the time-space evolution of the fire ball is described by the 2+1D viscous hydro model.At last,we use the Fast Jet program to recostruct the final-state jets with anti-kT algorithm.A relevant observable is the fraction(z?)of the jet momentum(pjet)carried by heavy quark along the jet axis direction.Based on the theoretical calculation of LO perturbation QCD+PS and considering the elastic and inelastic parton energy losses in the medium,we first studied the medium correction effect of the z? distribution of heavy quarks jets.By comparing z? in lead-lead collisions with proton-proton collisions,we find that heavy quarks lose less energy than light quarks and gluons when they traverse Quark-Gluon Plasma medium.We separately considered the situation where there is only collisional energy loss or radiative energy loss.Different values of spatial diffusion coefficient Ds have little affection on the peak of z? for heavy quarks jets.At higher traverse momentum,different values of jet transport coefficient q0 have little affection on the peak of z? for heavy quarks jets.By changing jet parameter R,we found that the smaller the value of the jet parameter R,the higher the peak value of z?,and the distribution becomes more concentrated.This trend is more visible to charm quarks jets than bottom quarks jets at higher transverse momentum.According to the distribution of z? of different centrality,we found that the energy loss of heavy quarks has some contribution to the total energy loss when the centrality is small.As the centrality becomes larger,the energy loss of heavy quarks has little affection on the distribution of z? for heavy quarks jets.